Limitations Of NAS
Although extremely useful devices, there
are some limitations to NAS drives. In larger networks with a high volume of
simultaneous I/O requests, a typical affordable NAS box is not going to be able
to provide adequate performance. Their built-in CPUs will be too limited in
performance and if over stretched will slow to a crawl. The CPU and network
hardware in a NAS is also rarely upgradable, because its single-purpose CPU is
hard-wired into the unit and the software stored on a firmware ROM chip. While
it's possible to spend a lot of money on more powerful NAS boxes with the
capacity to handle huge quantities of traffic, the lines between server and NAS
begin to blur considerably, especially in terms of cost.
Caringo
Smashes Limitations of Block-Based NAS
In a home environment, these limitations
are unlikely to be important, since high-volume simultaneous I/O traffic will
be rare. A limitation that will be more important is one of actual transfer
rate, as it's easy to fall into the trap of assuming a NAS box will be as fast
as an internal hard drive. Although some NAS boxes offer great performance,
some will only transfer data at 5-IOMB/s or, in the case of some manufacturers'
offerings, even less than this. While this kind of transfer rate will not be a
problem for streaming SD video to a single system, it won't have the bandwidth
available to serve two streams simultaneously. Even for the best NAS boxes, you
will need to invest in your home network infrastructure to ensure that the
transfer rate is not limited by the 100Mbps networks most of us use at home.
This situation only becomes slower if you are limited to wireless.
These limitations in speed are not caused
by the hard drive technology within, because even a modest 7200rpm hard drive
can sustain transfer rates of well over 100MB/s. Many NAS drives boast of a
'fast SATA interface' or 'gigabit connection', and yet still fall well short of
even 100Mbps network performance. This limitation is caused by a bottleneck at
the NAS drive's CPU, which can only process data requests so fast. Seeing as
these are a tiny fraction as powerful as the CPU at the heart of your home PC,
it's not entirely surprising you don't get the same level of performance. In
this day and age of ultra- fast computers, it's easy to forget just how much
overhead is required for good performance over a proper network!
Making Use Of Old Drives
Many enthusiast users have more than one
spare hard drive knocking around, in which case these can be recalled to
service as a NAS solution. Almost all NAS manufacturers offer drive-free
caddies that will allow you to plug in an existing SATA drive and convert it to
NAS duties. Some of these are extremely affordable, costing less than $80. You
invariably get what you pay for, however, so be sure to read some reviews
before parting with your cash. We've tested some cheap NAS enclosures before
that feature shockingly slow firmware, appalling transfer rates and unreliable
software. One of our favourite enclosures is the Synology DS110J, a single bay
drive-less enclosure with outstanding software and performance. These
enclosures can achieve over 60MB/s in read and around 40MB/s in write when
connected to a suitable gigabit network - impressive for such a modest asking
price. They have been replaced in Synology's line-up with the newer DS112J,
meaning they can be snapped up for a bargain price of less than $128 if you
shop around!
If you do need new drives to go with your
NAS, however, don't automatically assume you'll always get a better deal by
sourcing the enclosure and the drives separately. Since the hard drive crisis
hit, we've seen several cases where it's actually cheaper to buy a NAS with the
drives you need rather than source the constituent components separately.
As most NAS drives are bottlenecked by the
speed of your network or by the performance of their own internal processing
and memory constraints, you don't need to invest in extremely fast hard disk
drives to maximise their performance. It's much better to invest in drives that
prioritise quietness, reliability and power efficiency like the Western Digital
Caviar Green or Samsung 5900rpm Ecogreen products. These drives still provide
100MB/S+ performance when reading or writing, which is more than enough for a
NAS application. They're also significantly quieter than 7200rpm models and
will save power as well. Most of us leave NAS boxes permanently turned on, so
although a 3-4W saving in power isn't that relevant in the scope of running a
desktop PC, it's valuable for a NAS, which is designed to be left on 24/seven.
All too often we see even professional reviewers recommending faster hard
drives for improved NAS performance when in actual fact this will almost never
make any difference to the performance of your device.
NAS Noise And Power
The low noise level and power consumption
of NAS drives is a major attraction compared to a server, but that doesn't
necessarily make them silent.
Most multi-drive NAS boxes have at least
one cooling fan to keep the drives happy, with larger units usually
incorporating several. Conversely, most single-drive NAS units do not require
fans, because the thermal dissipation of just a single disk can be capably
handled passively.
If you're concerned with your green
credentials, try to choose a NAS that has built-in power saving. This will
allow it to power down the drive(s) when the unit isn't being accessed,
reducing consumption by however much power is being consumed to keep the
drive motors running (typically 8-12W per drive depending on the model being
installed).
